1. Field of the Invention
The present invention relates to an antenna device in which a slot antenna which excites a radiation slot formed in a metal plate and a circuit board having high frequency circuits connected to the slot antenna through a power feeding member are integrally formed, and more particularly, to a structure of the power feeding member.
2. Description of the Related Art
In this type of an antenna device, power feeding is implemented by forming a radiation slot in a metal case which covers a circuit board, thus allowing the case to function as a slot antenna. Therefore, the antenna device is suitable for a vehicle because miniaturization and cost reduction can be easily achieved.
FIG. 5 is a perspective view of a slot antenna according to the related art (for example, see JP-A-2003-218629 (page 2, FIG. 5). This slot antenna is constructed such that a radiation slot 2 is formed in an upper plate 1 a of a case member 1 made of a conductive metal plate so as to be excited. The radiation slot 2 is formed of an elongated aperture having a straight shape. Power feeding points 3 and 4 are set on the upper plate 1a at a substantially middle portion of the radiation slot 2. One of the power feeding points 3 and 4 is connected to a power feeding circuit, and the other is connected to a ground. While a power is being fed, a high frequency current flows along the periphery of the radiation slot 2, thus exciting the radiation slot 2 with a predetermined frequency.
In the slot antenna according to the above-described related art, the case member 1 can be used as a shield case which covers a circuit board (not shown) by disposing the upper plate 1 a above the circuit board having high frequency circuits such as a low noise amplification circuit. Thus, the power feeding points 3 and 4 are electrically connected to a land on the circuit board through a power feeding member such as a power feeding pin, so that a compact antenna device can be realized by making the slot antenna and the circuit board into one unit.
However, in the antenna device having the above-mentioned structure, in order to electrically connect the power feeding points 3 and 4 of the upper plate 1a to the land on the circuit board, the power feeding member should be soldered to each of the power feeding points 3 and 4. Thus, solder connection work is not only complicated but also may cause connection defects due to excessively strong stress applied on a soldered portion of the power feeding member when displacement is generated in a relative position between the upper plate 1a and the circuit board. In particular, when this type of an antenna device is mounted in a vehicle, displacement may easily occur in the relative position between the upper plate 1a and the circuit board due to thermal expansion which is caused by external vibration and temperature changes. Thus, for example, whenever the distance between the upper plate 1a and the circuit board increases and decreases, strong stress is applied on the soldered portion of the power feeding member, thus causing soldering crack to easily occur.